Effect Of Dead Volume Research Articles

Effects of dead volume and inert sweep gas flow on photocatalytic hydrogen evolution over Pt/TiO2

In this study, the effects of dead volume and sweep gas flow rate on photocatalytic hydrogen production over Pt/TiO2 were examined to determine their possible impact on hydrogen production rates. Five different dead volumes (15, 45, 75, 190, 425 ml) under constant reaction solution and interfacial area experimented by using custom made reactors. It was found that higher dead volumes in the gas phase inversely affect the measured hydrogen production. The difference between highest and lowest H2 production rates (at steady state) among five dead volumes is found as 30 μmol/h gcat which is 24% of the highest rate. On the other hand, the difference due to sweep gas flow rates (15, 30, 45 ml/min Ar) was not as significant. It was concluded from these results that measured hydrogen production rate in photocatalytic systems depend strongly on the reactor size through gas phase dead volume and operational factors like sweep gas flowrate. The difference between highest and lowest hydrogen production rates for different dead volumes or sweep gas flow rates is too great to ignore when the average photocatalytic hydrogen production levels (∼500 μmol/h gcat) in the literature are considered. Uncertainties associated with these factors together with well-known difficulties in measurement (or reporting) of the amount of energy and the characteristics of light absorbed by the reaction solution make the comparison of results from different studies impossible. The results of this study confirm the need for standard protocols of measurement and testing in the photocatalysis field in general, and photocatalytic hydrogen production particularly.

Перспективы создания современных поршневых компрессоров с повышенной производительностью

The current level of performance of piston compressors, characterized by the delivery coefficient, is at the level of 0,7. Advanced designs have higher rates, reaching values of 0,8...0,85. However, the negative effect of dead volume prevents the performance level of, for example, screw compressors from being achieved. Therefore, reducing the influence of dead volume on productivity can be considered the main task in improving modern piston machines. The presented work proposes a solution to eliminate the influence of the most significant component of the dead volume — linear space. As experimental studies have shown, the use of elastic discs mounted on the piston will virtually eliminate linear dead volume, ensure operational safety and increase the flow rate to 14 %.

10 clinical tips for advancing patient safety when using syringe pump systems for microinfusion intravenous drug therapy.

10 clinical tips for advancing patient safety when using syringe pump systems for microinfusion intravenous drug therapy.

Experimental and Monte Carlo-based determination of magnetic field correction factors in high-energy photon fields for two ionization chambers.

The integration of magnetic resonance tomography into clinical linear accelerators provides high-contrast, real-time imaging during treatment and facilitates online-adaptive workflows in radiation therapy treatments. The associated magnetic field also bends the trajectories of charged particles via the Lorentz force, which may alter the dose distribution in a patient or a phantom and affects the dose response of dosimetry detectors. To perform an experimental and Monte Carlo-based determination of correction factors , which correct the response of ion chambers in the presence of external magnetic fields in high-energy photonfields. The response variation of two different types of ion chambers (Sun Nuclear SNC125c and SNC600c) in strong external magnetic fields was investigated experimentally and by Monte Carlo simulations. The experimental data were acquired at the German National Metrology Institute, PTB, using a clinical linear accelerator with a nominal photon energy of 6 MV and an external electromagnet capable of generating magnetic flux densities of up to 1.5 T in opposite directions. The Monte Carlo simulation geometries corresponded to the experimental setup and additionally to the reference conditions of IAEA TRS-398. For the latter, the Monte Carlo simulations were performed with two different photon spectra: the 6 MV spectrum of the linear accelerator used for the experimental data acquisition and a 7MV spectrum of a commercial MRI-linear accelerator. In each simulation geometry, three different orientations of the external magnetic field, the beam direction and the chamber orientation were investigated. Good agreement was achieved between Monte Carlo simulations and measurements with the SNC125c and SNC600c ionization chambers, with a mean deviation of 0.3% and 0.6%, respectively. The magnitude of the correction factor strongly depends on the chamber volume and on the orientation of the chamber axis relative to the external magnetic field and the beam directions. It is greater for the SNC600c chamber with a volume of 0.6cm3 than for the SNC125c chamber with a volume of 0.1 cm3 . When the magnetic field direction and the chamber axis coincide, and they are perpendicular to the beam direction, the ion chambers exhibit a calculated overresponse of less than 0.7(6)% (SNC600c) and 0.3(4)% (SNC125c) at 1.5 T and less than 0.3(0)% (SNC600c) and 0.1(3)% (SNC125c) for 0.35 T for nominal beam energies of 6 MV and 7MV. This chamber orientation should be preferred, as may increase significantly in other chamber orientations. Due to the special geometry of the guard ring, no dead-volume effects have been observed in any orientation studied. The results show an intra-type variation of 0.17% and 0.07% standard uncertainty (k=1) for the SNC125c and SNC600c, respectively. Magnetic field correction factors for two different ion chambers and for typical clinical photon beam qualities were presented and compared with the few data existing in the literature. The correction factors may be applied in clinical reference dosimetry for existing MRI-linearaccelerators.

The effect of dead volumes on the performance of magnetic refrigerators

Regenerative magnetic refrigeration at room temperature has the potential to overcome various problems affecting vapor compression devices while providing competitive performance, but the effects of several loss mechanisms must be evaluated and accounted for. In actual devices, inactive sections in the regenerator originate dead volumes leading to possible non-optimal exploitation of the magnetocaloric material and the associated loss mechanism. While magnetic refrigeration gained attention, few studies have systematically investigated the effects of dead volume on system performance. In this work, a one-dimensional model valid for a generic magnetic refrigerator device (either linearly reciprocating or with continuous, or discontinuous, rotary motion) is used to study the effect of the dead volume. The device performance was assessed by comparing the characteristic curves (cooling power, and COP) of an ideal device (zero dead volume) to the corresponding characteristic curves for different dead volume ratios. The performance is negatively affected if the device is operated under the same working conditions and control parameter settings used in the ideal device. This effect is higher for higher temperature spans. Nevertheless, the device could approximate the ideal performance by adjusting its control parameters. The main measures to mitigate the negative effects of dead volumes can be summarized in the necessity to operate at lower frequencies, higher fluid mass flow rates, and higher torque. The results of this study prove that the proper control of such operative parameters is able to maximize the device performance and mitigate the performance losses due to the dead volume effects.

The dead volume effect on the elastic moduli measurements using the forced‐oscillation method

ABSTRACTIn low‐frequency laboratory experiments conducted on fluid‐saturated rocks, the boundary conditions of rock samples can significantly affect the results of the measurements of elastic moduli and acoustic attenuation. Generally, in laboratory measurements, the dead fluid volume associated with the fluid storage formed by the segments of the fluid line adjacent to a rock specimen cannot bе completely eliminated. Depending on the size, this fluid storage can significantly affect the elastic moduli measurements. We investigate the impact of the dead volume on (i) the quasistatic measurements of the elastic moduli of a fully fluid‐saturated rock specimen and (ii) the dispersion and attenuation measurements conducted on the same specimen at seismic frequencies. We present the results of the laboratory tests conducted at seismic frequencies on an n‐decane–saturated porous rock with the dead volume gradually changed from 2 to 260 cm3, as well as with the open‐pore‐fluid line. To take into account the dead volume, we developed a modified Gassmann theory and demonstrated that predictions of this theory are in good agreement with the measurements at lower frequencies. The Young's modulus dispersion and extensional attenuation observed at higher frequencies were explained on the basis of a one‐dimensional model considering the guided slow P‐waves in the rock specimen with boundary conditions specific to the experiment.

Lag times to steady state drug delivery by continuous intravenous infusion: direct comparison of peristaltic and syringe pump performance identifies contributions from infusion system dead volume and pump startup characteristics.

Time lags between the initiation of a continuous drug infusion and achievement of a steady state delivery rate present an important safety concern. At least 3 factors contribute to these time lags: (1) dead volume size, (2) the ratio between total system flow and dead volume, and (3) startup delay. While clinicians employ both peristaltic pumps and syringe pumps to propel infusions, there has been no head-to-head comparison of drug delivery between commercially available infusion pumps with these distinct propulsion mechanisms. We quantified the delivery of a model drug by peristaltic and syringe pumps at clinically relevant flow rates using spectrophotometric absorbance. Delivery curves were modeled and compared, and the time required to reach 5% (T5), 50% (T50), and 95% (T95) of the intended delivery rate was reported. The ability to overcome the combined effects of startup delay and dead volume differed between syringe and peristaltic pumps. T5, T50, and T95 were shorter for the peristaltic pump at higher flow rates. T50 and T95 were shorter for the syringe pump at lower flow rates. The ability to overcome the effects of dead volume was overall similar between the syringe and peristaltic pumps, as was the response to consecutive changes in drug infusion rates. Startup delay and dead volume in carrier-based infusion systems cause substantial time lags to reaching intended delivery rates. Peristaltic and syringe pumps are similarly susceptible to dead volume effects. Startup performance differed between peristaltic and syringe pumps; their relative performance may be dependent on flow rate.

Supporting Information for the dead volume effect in the elastic moduli measurements using the forced-oscillation method

Supporting Information for the dead volume effect in the elastic moduli measurements using the forced-oscillation method

A Laboratory Forced-Oscillation Apparatus for Measurements of Elastic and Anelastic Properties of Rocks at Seismic Frequencies

In presented paper, we describe the technical and physical aspects of the application of a low-frequency (LF) apparatus based on a longitudinal type of forced oscillations. In particular, we investigate the influence of the strain gauge position on a tested sample on measurement results, we also examine the creep effect associated with the mineralogy of rocks, as well as the dispersion and attenuation in a liquid-saturated rock sample caused by the presence of the volume of pore fluid exterior to the sample (dead volume). The effect of the position of the strain gauges is investigated using a cylindrical acrylic sample and two pairs of strain gauges fixed in the middle and at one of the sample ends under a uniaxial pressure of 15 MPa. The obtained results demonstrate that elastic and anelastic parameters of the tested sample are independent from the location of the strain gauges. The impact of the creep phenomenon on elastic moduli was studied using three room-dry samples of Savonnieres limestone, Berea sandstone and Eagle Ford shale. The measurements were conducted for 120 h at a frequency of 2 Hz under a uniaxial pressure of 10 MPa and demonstrated that the LF moduli of all rocks were noticeably reduced with time. The effect of dead volume was investigated at seismic frequencies using limestone saturated with n-decane. It was found that the Young’s and bulk moduli exhibit strong dispersion at frequencies above 10 Hz if the dead volume is close to or greater than the pore volume of the sample. We also found that the characteristic frequency of dispersion corresponding to the attenuation peak is independent of the size of the dead volume and determined only by the physical parameters of the sample and pore fluid. We present also the results of the Young’s modulus and attenuation measurements conducted at seismic frequencies on vertical and horizontal shale samples saturated with water. It was shown that the relationship between the extensional attenuation and the Young’s modulus dispersion observed in the samples saturated at a relative humidity of 97.5% is consistent with the Kramers–Kronig relation.

Stirling Thermodynamics using Phasor Notation

Phasor mathematics is used to develop the isothermal Stirling cycle and extended to the ideal adiabatic Stirling cycle. The results are developed for piston – piston (alpha) machines and displacer – piston (beta and gamma) machines. The effect of non-ideal regeneration is handled by defining a regenerator effectiveness ratio. The importance of the amplitude pressure ratio (pressure amplitude to the mean pressure) is developed and shown to be a useful parameter when evaluating the effect of dead volume or when applying simple cycle analyses. The analysis is developed for both power producing and cooling engines. The utility of these analyses is discussed with respect to calibrated results of real machines.

Numerical simulation of the dead-volume effect in seismic-frequency measurements of elastic properties of fluid-saturated rocks

Low-frequency measurements of the elastic properties rocks based on the forced-oscillation method is an emerging approach for calibration of well log and seismic measurements. The dispersive proper...

The myth about dead volume in Stirling engines

The effect of dead volume on the power output and efficiency of an alpha-Stirling engine is investigated in the form of an exploratory parameter study using the third-order simulation software Sage. This paper aims at identifying the underlying mechanisms in order to better understand the resulting design implications of this phenomenon that is in clear contradiction to what can be found in the literature. It turns out that additional ‘passive’ dead volume that does not even take part in the heat transfer processes leads to a phase shift of the pressure, resulting in increased pV-work output, especially at lower heat source temperatures. Of even greater significance, dead volume has a positive effect on the efficiency at lower heat source temperatures by reducing the temperature swing in the heat exchangers and by bringing the gas temperatures closer to the wall temperatures of the respective heat exchangers, and thus increasing the effective temperature difference. Furthermore, to a large extent the beneficial effects of dead volume can also be achieved by changing the phase angle.

Adsorption equilibrium and kinetic study of guaifenesin enantiomers on cellulose tris 3,5-dimethylphenylcarbamate packed column

The chromatographic separation of guaifenesin enantiomers using hexanes/ethanol mobile phase and cellulose tris 3,5-dimethylphenylcarbamate stationary phase (Chiralcel OD) was investigated, where the column was packed with particle size 20μm of chiral adsorbents. The adsorption equilibrium isotherms of single enantiomer and racemic compounds of guaifenesin on Chiralcel OD stationary phase were measured by the frontal analysis and the adsorption–desorption method, respectively. Then, the experimental data were fitted with the Linear+Langmuir isotherm model, and the relative model parameters for the competitive adsorption equilibrium isotherm of guaifenesin enantiomers were obtained by the nonlinear regression method. Both the elution and adsorption–desorption experiments for the separation of guaifenesin enantiomers on the Chiralcel OD packed column were carried out. The measured elution curves and adsorption–desorption profiles were compared with the theoretical predictions by mathematical model, and adsorption kinetics, separation efficiency, the effect of dead volume were discussed. According to experiments and modeling, the competitive adsorption equilibrium and kinetics information were acquired for the scale up and optimization of the separation of guaifenesin enantiomers by both batch and continuous chromatographic system.

Development of the tandem reciprocating magnetic regenerative refrigerator and numerical simulation for the dead volume effect

In this paper, the development of the tandem reciprocating room-temperature active magnetic regenerative refrigerator and the numerical simulation for the effect of the dead volume are presented. The dead volume effect is analyzed by establishing a one-dimensional time-dependent model for the active magnetic regenerator (AMR). The cooling power at the mass flow rate of 5 g s−1 water and a temperature span of 20 K is reduced from 4 W to 2 W when the length of the dead volume (DDV = 12 mm) is increased from 15 mm to 30 mm. The numerical results indicate that the minimization of dead volume facilitates the improvement of the AMR performance. In particular, the components and the parameters of AMR system are demonstrated. The printed circuit heat exchangers (PCHEs) are employed as the warm end heat exchangers in order to minimize the dead volume of the system. The experimental apparatus includes two active magnetic regenerators containing 186 g of Gd spheres. The maximum no-load temperature span of 26.8 K and a maximum cooling power of 33 W at a zero temperature span were obtained with the frequency of 0.5 Hz under the maximum field of 1.4 T.

Calibration of RaDeCC systems for 223Ra measurements

RaDeCC (or radium delayed coincidence) counters have proved to be a fast and precise way to measure 224Ra and 223Ra in water samples. However, the calibration of these counters for 223Ra has been problematic. Unlike standards prepared from 232Th to calibrate 224Ra–220Rn measurements, standards prepared from 227Ac for 223Ra–219Rn measurements decrease in the amount of 219Rn they release with time. Here we develop a way to use the 232Th calibration of the 220 channel efficiency to calibrate the 219 channel. We first consider the slightly different effects of delay and window opening time constants in the default RaDeCC system. These differences favor 220Rn detection by about 3%. Next, we consider the effect of dead volume on the relative efficiencies. In a typical system, with a source volume in the range 100–300ml, there is about a 3–8% lower predicted probability of 219Rn decaying in the counting cell relative to 220Rn. Thus, the absolute efficiency of the 219 channel should be about 6–11% lower than the efficiency of the 220 channel, depending on the dead volume of the system. We tested the effects of window time constants and dead volumes by altering these parameters in a known manner and correcting for the alterations. In this analysis we neglect the differences in alpha decay energy between the 219Rn–215Po pair and the 220Rn–216Po pair. These differences may increase slightly the efficiency of the 219 channel because of the higher alpha decay energies of 219Rn–215Po.

Development of an In Situ pH Calibrator in Deep Sea Environments

The pH Calibrator is an instrument for in situ calibration and measurement of chemical species (pH) in aqueous fluids at elevated pressure. The calibration device consists of two interactive systems: a data-logging sensor system and an automated fluid de- livery system. The solid-state pH sensor array is sealed in a flow cell to decrease measurement response time. The automated fluid de- livery system consists of a pump and process control valves, which intermittently deliver seawater samples for measurement. Following measurement cycles, the pH buffer solutions are drawn into the sensor cell to perform two-point calibration. Here, we describe the initial steps in its conversion from a battery-powered instrument for short-term application into a unit that can be used to take full advantage of cabled-powered observatories that will soon be coming online at a number of locations in marine environments. Accordingly, we made use of the continuous power supply and TCP/IP network capability intrinsic to the Monterey Accelerated Research System (MARS)-cabled ocean observatory, Monterey Bay, CA, to reconfigure the unit in anticipation of future seafloor deployments. The flow through system has been further optimized to reduce dead volume effects in the calibration process, while the mechanical system can now better tolerate increases in fluid discharge pressure and flow rate for long-term operations. Furthermore, the sensor head is now equipped with a novel valve to enhance operations in hydrothermal diffuse flow environments. To gain full access to the MARS-cabled observatory, the dc-dc power converter module and Ethernet to serial module are integrated to the electronics. The pH Calibrator has passed the wet node simulator tests in a seawater tank at the Monterey Bay Aquarium Research Institute, moving the project closer to fulfilling long-term objectives for marine studies.

Effect of dead volume on performance of simulated moving bed process

The volume of surrounding equipments (pipe transfer lines and valves) in the simulated moving bed (SMB) unit, which is called the dead volume, is modeled as bed-head, bed-tail and bed-line. Since the dead volume can be significant especially in industrial-scale SMB units, the consideration of dead volume has been required for high performance operation. In this study, a simple and unified approach based on the method of characteristics (MOC), called the extended node model, is established to solve fluid concentration dynamics within dead volumes. The computational efficiency of the approach is evaluated for three case studies of a standard four-zone SMB process with a linear adsorption equilibrium model. Insertion of one zone to flush the fluid trapped in extract bed-line into the standard four-zone SMB improves substantially purity, while recovery is kept constant.

Thermodynamic analysis of a Stirling engine including regenerator dead volume

This paper provides a theoretical investigation on the thermodynamic analysis of a Stirling engine with linear and sinusoidal variations of the volume. The regenerator in a Stirling engine is an internal heat exchanger allowing to reach high efficiency. We used an isothermal model to analyse the net work and the heat stored in the regenerator during a complete cycle. We show that the engine efficiency with perfect regeneration doesn’t depend on the regenerator dead volume but this dead volume strongly amplifies the imperfect regeneration effect. An analytical expression to estimate the improvement due to the regenerator has been proposed including the combined effects of dead volume and imperfect regeneration. This could be used at the very preliminary stage of the engine design process.

New insights into the formation of volatile compounds in mainstream cigarette smoke.

A sampling system has been set up to monitor a group of volatile smoke analytes (nitric oxide, acetaldehyde, acetone, benzene, toluene, 1,3 butadiene, isoprene and carbon dioxide) from mainstream cigarette smoke on a puff-resolved basis. The system was able to record gas evolution profiles during puffing and interpuff periods without interruption (e.g. taking clearing puffs). Gas phase smoke analytes were sampled as close to the mouth end of the cigarette filter as possible in order to minimise any dead volume effect. The results revealed that, for some volatile species, a significant fraction (e.g. up to 30% for benzene) in the cigarette mainstream smoke had been generated during the preceding smoulder period. These species were trapped or absorbed within the cigarette rod and then subsequently eluted during the puff. The identification of the two sources of the mainstream smoke, a smouldering source and a puffing source, has not been reported before. The observation contributes to the fundamental knowledge of the cigarette smoke formation and may have implications on wider smoke chemistry and associated effects. FigureA cross-sectional schematic of a burning cigarette, illustrating the main chemical and physical processes involved in the smoke formation

First and second law analysis of a Stirling engine with imperfect regeneration and dead volume

This article discusses the thermodynamic performance of an ideal Stirling cycle engine. This investigation uses the first law of thermodynamics to obtain trends of total heat addition, net work output, and thermal efficiency with varying dead volume percentage and regenerator effectiveness. Second law analysis is used to obtain trends for the total entropy generation of the cycle. In addition, the entropy generation of each component contributing to the Stirling cycle processes is considered. In particular, parametric studies of dead volume effects and regenerator effectiveness on Stirling engine performance are investigated. Finally, the thermodynamic availability of the system is assessed to determine theoretical second law efficiencies based on the useful exergy output of the cycle. Results indicate that a Stirling engine has high net work output and thermal efficiency for low dead volume percentages and high regenerator effectiveness. For example, compared to an engine with zero dead volume and perfect regeneration, an engine with 40 per cent dead volume and a regenerator effectiveness of 0.8 is shown to have ∼60 per cent less net work output and a 70 per cent smaller thermal efficiency. Additionally, this engine results in approximately nine times greater overall entropy generation and 55 per cent smaller second law efficiency.